The design of electronic circuits has become increasingly complex with the advent of microprocessor-based systems. Troubleshooting such circuits demands instruments that can capture simultaneous digital signals and display their analog characteristics. Conventional oscilloscopes that are quick enough to view the subnanosecond pulses of these signals lack the capability to trigger on a combination (referred to as a word) or series of combinations of these signals. Logic analyzers, on the other hand, excel at triggering on words. But they lack an oscilloscope's ability to display the voltage and timing characteristics of the digital signals that form the word.
Several attempts have been made to address this demand by incorporating the measurement capability of the oscilloscope and the recognition capability of the logic analyzer into a single device. Devices of this type include the 7A42, an oscilloscope logic triggered amplifier manufactured by Tektronix, Inc., of Beaverton, Oreg., and now the subject of U.S. patent application Ser. No. 06/487,398, now U.S. Pat. No. 4,585,975; the Microanalyst, a timing analyzer manufactured by Northwest Instruments, Inc., of Beaverton, Oreg.; and the 54100D, a digital oscilloscope manufactured by Hewlett-Packard Company of Palo Alto, Calif. These devices vary from each other primarily in the triggering modes they offer.
The 7A42 is designed to trigger on a single word or a nested sequence of Boolean words and to display the corresponding analog characteristics of the signals that form each word. In the single word combination of inputs, it can trigger either immediately on the appearance of a predetermined combination or after the combination has persisted for a predetermined time. In the nested mode, it triggers on the appearance of a sequence of a first predetermined combination followed immediately by a second predetermined word combination.
The Microanalyzer lacks an analog display of the digital signals but offers other triggering modes not found in logic analyzers or the 7A42. In addition to the single word and nested triggering modes, it can trigger on a digital signal that is detected between predetermined logic levels within a predetermined time of a clock pulse.
The 54100D offers analog signal display capability and includes several triggering modes not available in the instruments above. Like the logic analyzer and other devices, it can trigger on a single word, both immediately and after the word's persistence for a predetermined time. The 54100D can also detect and trigger on a narrow pulse, or glitch, and display the pulse's analog characteristics. In addition, it can be set to trigger after the occurrence of a predetermined number of events or a predetermined time. However, it cannot trigger on nested sequence of word combinations without the aid of a logic analyzer.
These devices are great improvements over what was previously possible with a conventional logic analyzer or oscilloscope. But they lack the capability of triggering in many other circumstances where it is desirable to view the analog characteristics of the signals within a system. For example, none of them can detect and display the analog characteristics of a plurality of digital signals transitionally between high and low logic levels. Nor can they detect a sequence of a first predetermined word combination followed by one of two second predetermined combinations. They also cannot detect a sequence of a first predetermined combination followed by the absence of one of two second predetermined combinations. And none of these devices offers all these triggering modes in a single device that can monitor up to eight input signal channels simultaneously.